Disclosed are an electrophotographic apparatus having a web fuser and corresponding methods.
In a typical electrophotographic or electrostatographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roller or to a latent image on the photoconductive member. The toner attracted to a donor roller is then deposited as latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat and pressure, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rollers with the toner image contacting the heated fuser roller to thereby effect heating of the toner images within the nip. In a conventional two roll fuser, one of the rolls is typically provided with a layer or layers that are deformable by a harder opposing roller when the two rollers are pressure engaged.
Web fusers are a type of toner image fixing device in which a web is looped around a fuser roller and typically conveyance rollers. A belt could be used in place of the web, where typically a belt is endless forming a loop, while a web has two ends each of which may be connected to a spool. A pressure roller presses a sheet having a toner image onto the fuser roller with the endless belt intervening between the pressure roller and the fuser roller. The fixing temperature for the toner image is controlled on the basis of the temperature of the fuser roller which may be detected by a sensor, such as a sensor in the loop of the belt and in contact with the fuser roller. A nip region is formed on a pressing portion located between the fuser roller and the pressure roller. The web or a belt fuser is typically short as the fuser assembly is often enclosed within a cassette, and it is desirable that such a fuser cassette is as small as possible.
The primary failure modes of such web fusers which represent the largest contribution to fuser run cost are typically attributed to the life of the fuser web or member. The fuser web comes into contact with the toner during the fusing process, and greatly influences the final quality of the print. Imperfections can form in the web including edgewear, toner offset, scratches, coating defects, and the like. It would be desirable to reduce the onset rate of these failure modes and/or to avoid toner contact with any damaged portion of the web once damage occurs, to increase the life of the web and fuser assembly.